docs: add metagraph-module and forward-look architecture specs, remove SchemaBuilder legacy support

Graph type definitions as TypeBox Modules — the core architecture evolution
for @alkdev/storage. The SchemaBuilder is removed (no existing consumers),
replaced by direct TypeModule construction with Metagraph.Import() for
base attribute composition and Type.Composite() for node/edge type
specialization.

Key additions:
- metagraph-module.md: Module pattern, edge constraints as named entries,
  SchemaBuilder equivalence, DB bridge contracts (moduleToDbSchema return
  type, validateNode/validateEdge signatures), 10 design decisions (DD1-DD10)
- forward-look.md: pointer abstraction (ujsx ValuePointer analogy, JPATH
  Module), dbtype table rendering relationship, ujsx as universal IR pipeline

Critical corrections from architecture review:
- Type.Composite uses IntersectEvaluated (intersection, not Object.assign
  override) — overlapping keys with subtype relationships resolve correctly
- Type.Ref inside Type.Composite within a Module is verified working
- BaseNode/BaseEdge use Metagraph.Import() for same-package Modules (Option B),
  not local re-declaration (no circular dep within same package)
- Edge constraints use Type.String() for node type name arrays (not Type.Ref) —
  constraints contain names, not schemas

AGENTS.md

@@ -16,7 +16,7 @@ instances) from the earlier `@ade` prototype.
 ├── mod.ts                   # Re-exports graphs/ only (zero db deps)
 ├── deno.json                # JSR config, imports, tasks, lint rules
 ├── src/
-│   ├── graphs/              # Schema types + SchemaBuilder (no db deps)
+│   ├── graphs/              # Metagraph Module + bridge functions (no db deps)
 │   ├── sqlite/              # SQLite host (drizzle-orm/libsql)
 │   │   ├── tables/          # Drizzle table definitions
 │   │   ├── relations.ts     # Drizzle relations
@@ -28,7 +28,7 @@ instances) from the earlier `@ade` prototype.
 
 ### Subpath Exports (JSR/npm)
 
-- `@alkdev/storage` → graphs types + SchemaBuilder (zero deps)
+- `@alkdev/storage` → Metagraph Module, graph type definitions (zero deps)
 - `@alkdev/storage/sqlite` → SQLite tables, relations, client (drizzle-orm +
   libsql)
 - `@alkdev/storage/pg` → PostgreSQL tables, relations, client (NOT YET
@@ -79,6 +79,7 @@ Key changes from the originals:
   `GRAPH_STATUS`)
 - `client.ts` refactored to be injectable
 - Module-level `db` and `client` exports removed
+- `SchemaBuilder` removed — replaced by `Type.Module()` construction
 
 ## File Conventions
 
@@ -99,6 +100,10 @@ See `docs/architecture/` for detailed specifications:
 - `overview.md` — Package purpose, exports, design decisions, open questions
 - `metagraph.md` — Core graph model, schema types, SchemaBuilder, attribute
   storage
+- `metagraph-module.md` — Graph type definitions as TypeBox Modules (evolution
+  of metagraph.md), naming conventions, migration path
+- `forward-look.md` — Connections to dbtype, graph pointers, ujsx universal IR
+  pipeline
 - `sqlite-host.md` — SQLite tables, relations, client factory, porting notes
 - `encrypted-data.md` — Encrypted data design (planned), crypto utility, node
   type modeling